Hollow sleeve augment device and tool

ABSTRACT

An augment device includes a hollow sleeve surrounding a channel extending through the hollow sleeve from a top to a bottom of the hollow sleeve, the hollow sleeve comprising a wall having an inner face and an outer face. The hollow sleeve includes at least one bending joint, the bending joint being configured for compressing the channel. Thereby the hollow sleeve may be compressed under an external force, leading to a decreased circumference and width of the hollow sleeve. This leads to a gap between the perimeter of the augment device and surrounding bone material, breaking any connections, By virtue of this, a much facilitated removal of the augment device can be achieved. Further, an extraction tool includes grippers for engaging and compressing the augment device, and further instruments, particularly a jig, for achieving an effective removal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of prior-filed U.S. patentapplication Ser. No. 15/742,697, filed Jan. 8, 2018, which is a nationalstage application under 35 U.S.C. 371 of International PatentApplication No. PCT/EP2016/064728, filed Jun. 24, 2016, which claimspriority to European Application No. 15176128.5, filed Jul. 9, 2015, allare hereby incorporated by reference in the present disclosure in theirentirety.

FIELD OF THE INVENTION

The invention relates to an augment device for a joint endoprosthesisand to a tool for this augment device, and more specifically to a tibialaugment for a knee joint endoprosthesis.

BACKGROUND OF THE INVENTION

Due to diseases, injuries or wear, particularly due to high age,replacement of joints in a body, such as knee, shoulder, elbow, withendoprothetic implants is common. Due to other illness or due to anexplanting of a failed endoprosthesis it is not uncommon to find animplantation site for the endoprosthesis which is pathologic, mainly dueto bone defects in its vicinity. This is a problem for the surgeonssince a lack of strong bone near the joint implantation side couldrender implantation of the endoprosthesis impossible or could lead topremature failure. Since such bone defects are encountered quite often,various approaches to remedy the situation have been devised.

In particular for such indications, wherein a joint endoprosthesis is tobe used, it is known to provide an augmentation device which isconfigured to fill a gap left by defective bone. Such an augmentationdevice having the form of a hollow sleeve is e.g. disclosed in U.S. Pat.No. 8,506,645 B2. Accordingly, defective bone material will be removedand the cavity created thereby will be filled by placing of the augmentdevice. The shape of a hollow sleeve serves a purpose of allowing thestem of a stemmed endoprosthesis to pass through its central opening,which forms a channel for the stem. The hollow sleeve itself isconfigured to be impacted into the cavity.

While a firm seating of the implant device is generally advantageous forlong-term stability, there is a drawback in that any removal would bedifficult if after some time such a need for removal were to arise. Infact, there exists a conflict of interest, firm seating of the implantdevice at one hand and ease of removal in case of need at the otherhand.

SUMMARY OF THE INVENTION

According to some embodiments, an improved augment device and tool easeremoval without compromising fixation strength.

In an augment device, in particular a tibial augment for a knee jointendoprosthesis, comprising a hollow sleeve surrounding a channelextending through the hollow sleeve from a top to a bottom of the hollowsleeve, the hollow sleeve comprising a wall having an inner face and anouter face, the hollow sleeve according to the invention comprises atleast one bending joint, the bending joint being configured forcompressing the channel.

By virtue of the bending joint the hollow sleeve may be compressed undera force exerted from the outside, thereby achieving a decreasedcircumference and width of the hollow sleeve. The effects of this is aconsiderable improvement in both, achieving a firm seating andfacilitating removal.

Reducing the circumference enables the augment device to be put into atight cavity of the bone more easily.

Reducing the width of the augment device means that a gap between theouter face of the augment device and surrounding bone material and bonytissue will be formed, thereby facilitating cutting of any connectingbone and tissue material which bonds the augment device to thesurrounding bone. Depending on the rigidity of said bone tissue it willbreak under the compressive action of the augment device, therebyfreeing the augment device. But even if the connecting tissue were notto break the gap formed between the outer face of the augment device andthe surrounding matter facilitates insertion of a knife or a similarinstrument for cutting any bonding tissue, thereby effectively freeingthe augment device, too. As a result, for effecting a re-operation theaugment device to be removed will be put under compressive load, therebycompressing the augment device and reducing its overall width, forming agap to the surrounding tissue and breaking connections to thesurrounding tissue. Thereby the augment device will become free andcould be removed without inflicting further harm or damage to thesurrounding bone. Any re-operation which may become necessary will thusbe much easier since removal of the old implant device becomes mucheasier according to the present invention.

Since the cavity is often dimensioned to be rather tight for improvedmechanical stability of the augment device and the endoprosthesis in thebone, and further to preserve as much of healthy bone as possible, thereis a problem that forcing the augment device into a tight cavity maycreate a risk of a creating cracks in the bone. By virtue of the bendingjoint, the hollow sleeve could be compressed to a smaller size, therebyallowing it to be more easily placed into the cavity. Thereby a firmseating can be reached without risk for the patient.

However, there is a conflict of interests in firm seating of the augmentdevice at one hand and creating a reliable option for removing theaugment device in case of need. Such a need may arise subsequent to animplant operation, in particular if the augment device needs to beremoved due to disease (e.g. inflammation) or due to wear and tear. Aspecific problem encountered with augment devices as opposed to regularendoprostheses is that bony material grows into the augment device,which is in principle an advantage for a solid stabilization andfixation of the augment device, however that same ingrowth of bonymaterial contributes to complicating removal on the other hand. Asimilar problem arises due to usage of cement, which ensures goodfixation on one hand but it is a huge liability in terms of removal. Byvirtue of the invention, the hollow sleeve may be compressed in situ,thereby breaking any fixation achieved by cement or ingrowth of bonymaterial, leading to loosening and therefore facilitating removal.

As a result, the traditional contradiction of good fixation at one handand easy of removal at the other hand could be overcome. Preferably, twoor more bending joints are provided, which are further preferablyarranged in a mirror symmetric fashion. This allows for a more uniformcompression of the hollow sleeve. Further preferably the bending jointis configured to be elastic.

Preferably, the bending joint is formed by an integral hinge, thatfurther preferably comprises an elongated void in the hollow sleeve anda strip of solid material spanning the void. Preferably, the strip isoriented such as to be oblique with respect to the wall, furtherpreferably such that a lower end of the strip is positioned closertoward the outer face than an upper end of the strip which is positionedcloser toward the inner face. The strip acts as a hinge providing thedegree of movement required for bending a part of the hollow sleeve inrespect to the other part. Further, an axis of the hinge as formed bythe strip is defined by the orientation of the strip. Rather thanorienting the strip to parallel to a middle chord of the wall, it isoriented oblique to it. Thereby the bending axis will not be parallel tothe plane of the wall, instead it will be—in case of a generally conicalshape of the augment device—parallel or at least nearly parallel to acenter axis of the channel. The degree of oblique orientation is definedby the cone angle of the hollow sleeve. In other words, the obliquearrangement of the strip counteracts the effect of the conically formedwall and ensures a compressing in a horizontal plane parallel to the topcover.

In a further preferred embodiment, the strip is configured to have areduced bending stiffness in a lower portion, preferably by means of atapering width. Owing to the lower bending stiffness the contribution ofthe lower portion to the overall bending stiffness is rather small. As aresult, the percentage reduction of the stiffness of a shorter bendingjoint is smaller than the percentage reduction of the length of thatbending joint where all bending joints—although having differentlengths—end at the top of the sleeve, e.g. at a hollow sleeve having astepped bottom. This allows shortening of the augment device at itsbottom without a significant effect on the bending stiffness of thebending joint in the shortened area.

Advantageously, at least one of the bending joints is arranged forenabling compression in an anterior/posterior direction. The terms“anterior” and “posterior” refer to directions of the augment device inwhich it is designed to be implanted to the human body. “Anterior”relates to a forward facing direction, and “posterior” to a backwardfacing direction. Similarly, at least one bending joint is arranged toenable compression in a lateral/medial direction. The term “lateral”refers to a direction substantial perpendicular to theanterior/posterior direction, namely to a direction away from the centeraway in a lateral direction, and “medial” refers to the oppositedirection toward the center. Further preferably, at least two bendingjoints are provided, at least one enabling compression in ananterior/posterior direction and at least one enabling compression in alateral/medial direction.

Further preferably, the hollow sleeve comprises a compensator elementconfigured for adjusting a circumference of the sleeve in a bended stateof the bending joint. The compensator element allows a degree of freedomfor absorbing a reduction of the circumference which will be realized bymoving the bending joints under compressive force. Preferably, thecompensator element is configured as at least two overlapping tonguesbeing in sliding relationship. Owing to the sliding relationship, thetongues maintain the bulkhead functionality even in the area of thecompensator element. Further, the sliding relationship allows a variancein length and thereby the reduction of the circumference.

The wall is preferably at least partially comprised of porous material.The porous material is configured for promoting bone ingrowth, therebyachieving a much improved fixation of the sleeve to the bone.

Preferably the hollow sleeve is provided with receptacles for grippermeans of a handling tool. Compressing the hollow sleeve requiresconsiderable force, in particular if bony material that had ingrownand/or cement bonding the augment device to surrounding tissue has to bebreak. Exerting such force usually exceeds the capabilities of pliers orsimilar tools, and applying brute force with a hammer would be too riskyfor the patient in terms of breaking bone. For a safe and easierhandling a special handling tool is provided, which features grippermeans that are configured for interaction with the hollow sleeve inorder to compress it. For providing a solid attachment of the grippermeans, the hollow sleeve is preferably provided with receptacles. In anadvantageous embodiment, the receptacles are configured as recesses fora form-fit to the gripper means. Thereby a positive engagement can beachieved. It is even further improved if the receptacles are configuredwith an undercut. By virtue of the undercut the handling tool can exertconsiderable pulling-out forces via the gripper means, without riskingthat the gripper means may leave there receptacles. It is to be notedthat the receptacles may be a separate structure, like a recess, or maybe realized by means of a porous portion into which the gripper meansengages, in particular if the gripper means are preferably provided withteeth.

It is preferred that the wall is configured as a sandwich structurehaving a solid portion and porous portion forming the outer face, theporous portion being formed of porous material which is configured foringrowth of bony material. By providing a porous portion on the outerface ingrowth of bony material is promoted and therefore an improvedattachment and fixation of the augment device to the surrounding bonewill be achieved. The same applies if cement is used as a bonding agent.Further, the porous structure may act as a receptable for being engagedby the gripper means of the handling tool.

Preferably alignment holes are provided on the top of the hollow sleevefor a proper attachment of any tools. Preferably, the alignment holesare being configured for positioning of the jig. By virtue of thealignment holes, a proper orientation of the tool, in particular thejig, can be achieved. The alignment holes provide a positive positioningof the tool, namely a jig, without requiring visual positioning. This isa considerable advantage, in particular if access to the location wherethe augment device is implanted should be difficult. Nevertheless,checking marks are preferably provided which are in a fixed spatialrelation to the alignment holes. The checking marks are being configuredsuch as to indicate proper positioning of the jig. A double-check can beperformed to ensure that the jig is positioned properly. The checkingmarks can be configured for visual and/or haptic verification.

In case the wall is made of a sandwich structure the top is preferablymade of solid material only and configured such that it coversessentially the complete upper side of the wall, which means the wallitself and a porous portion applied to its outer face, if such porousportion is provided. Thereby any unwanted influx of bony material orcement could be avoided. Preferably, the top and the wall form a unitaryelement.

According to a further embodiment of the invention, which may be thesubject of independent protection, an extraction tool for an augmentdevice as described above is provided, the extraction tool comprising asubstantially flat frame having a center portion and a peripheryportion, said frame defining a plane, a plurality of grippersdistributedly arranged at the periphery portion, the grippers havingengagement means for engaging the augment device, at least one of thegrippers be movable along said plane of the frame inward towards thecenter portion of the frame, and a compression element actuating the atleast one movable gripper. The grippers are configured such as to beenabled to attach to the augment device at its circumference, preferablyby engaging the receptacles of the augment device in a form-fit manner.By actuating of the compression element the movable grippers are movedinward, thereby compressing the augment device and reducing itscircumference and width. This reduction allows for an easier implantingand in particular removal of the augment device in respect to the bonewhere it is designed to be implanted. In particular regarding removal, acompressing of the augment device creates a gap between thecircumference of the augment device and the cavity in which it isseated, thereby breaking away bony structure or cement that was fixatingthe augment device to the surrounding bone material. Subsequent to thisbreaking away, the augment device could be removed much easier.Preferably at least three grippers are provided.

Preferably at least one gripper is stationary, and the movable gripperis configured to move towards said gripper which is stationary. Therebya gripping action could be effectively combined with an improvedpositive control of the positioning of the extraction tool and theaugment device gripped thereby. This enables a much more precisepositioning which minimizes potential damaging of surrounding tissue.Further preferably at least two movable grippers are provided, therebyachieving a wider grip with respect to the stationary gripper. Theextraction tool is thus enabled to engage a bigger variation of size ofaugment devices while still maintaining the increased positionalaccuracy achieved by the stationary gripper.

The grippers may be configured for a form fit co-operating with recessesat the outer face of the augment device, or the grippers could beprovided with teeth configured for piercing into the outer face of theaugment device.

In a preferred embodiment, the extraction tool comprises a V-shapedstationary sub-frame with at least one movable outrigger, each outriggercarrying at least one of the movable grippers. Preferably, a pluralityof outriggers are provided which are symmetrically arranged at thesub-frame. This allows for a compact configuration of the extractiontool. Further, the grippers are preferably located at corners of theframe, wherein the corners are being connected by edges of the frame. Itis particularly preferred to shape the frame such that its edges arebeing offset to the inward with respect to an envelope line connectingthe corners. Thereby free access to the outer face of the augment devicefrom above is achieved, allowing the surgeon to freely manipulate inthat area for clearing out any residual cement, bony ingrowth, or otherdebris surrounding the augment device. This further adds to an easierremoval.

For engaging the augment device, the grippers must reach below the topof the augment device in order to engage the outer wall. In an implantedstate the augment device is usually flush mounted, i.e. its side wallswith their outer face are not readily accessible. In order to provideaccess, holes must be formed at those places where the grippers shallreach down in order to engage the outer face of the wall. For a properpositioning of these holes, a jig is preferably provided. The jigfeatures a handle and a basic plate having guiding holes at its corners.These guiding holes serve for defining the positions at which the holesare to be drilled in order to provide access to the side wall of theaugment device. The positioning of the corners with the holes at the jigis the same as the positioning of the grippers at the extraction tool,whereas the grippers are in non-actuated (idle) position.

Further preferably, a holder is provided that can be engaged to theextraction tool. The holder may preferably comprise a striking weightthat could be employed to increase extraction power.

The invention further relates to a method of handling an augment device,as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described according to theaccompanying drawing in an exemplary manner. In the drawings:

FIGS. 1 a, b is an overview of a first exemplary embodiment;

FIG. 2 is a schematic view showing an augment device according to theinvention in situ;

FIGS. 3 a, b is a top and perspective view of a first embodiment havingbending joints;

FIG. 4 is a detailed cross section through one of the bending joints;

FIGS. 5 a, b is a top and perspective view of a second embodiment havingbending joints;

FIGS. 6 a, b are perspective views of a first and second embodimentshowing recesses and alignment holes;

FIG. 7 shows a detailed top view of an alignment hole as shown in FIG. 6b;

FIG. 8 shows the augment device and its alignments hole in relation to ajig in an implanted state;

FIGS. 9 a, b are top and perspective views of an extraction tool of theaugments devices;

FIG. 10 shows additional instruments complementing the extraction tool;

FIG. 11 shows a mutual relationship between the augment device, jig andextraction tool; and

FIGS. 12 a-h show steps of operation.

DETAILED DESCRIPTION OF THE INVENTION

A first embodiment of an augment device 1 according to the presentinvention is shown referring to FIGS. 1-4. The augment device 1 of thisembodiment is preferably a tibial augment which is made of abiocompatible metallic material. It is preferably selected from a groupcomprising titanium alloys, pure titanium, cobalt chromium, stainlesssteel, tantalum and zirconium. Further preferably, the material is puretitanium (for example Ti Grade 2). This combines excellentbiocompatibility with good strength and stiffness characteristics.Another preferred material is a titanium alloy (for example Ti6Al4V).This material is more regularly available, also it has a higherstiffness.

The tibial augment has a generally conic form of a hollow sleeve 10. Thehollow sleeve 10 comprises a wall 17 surrounding a channel 11 which runsentirely through the augment device 1 from its top 12 to its bottom 13.The channel 11 is configured for receiving a stem of an endoprosthesis,in particular the stem 94 of a tibial part 92 of a knee prosthesis 9.

The tibial augment 1 is configured such as to be anatomically sized andshaped to fill a cavity in an upper part of a distal bone 99, namely thetibia. The augment device 1 is formed generally conically for betterfitment. Its bottom side 13 is generally planar as well as its top 12.

As it can be appreciated in FIG. 2, the augment 1 is placed in thecavity of an upper portion of the bone 99, thereby forming a base onwhich a tibial plate 93 of the tibial component 92 of the kneeprosthesis 9 is to be positioned. The knee prosthesis 9 furthercomprises a femur component 91 configured for rotatable interaction withthe tibial portion 92. The tibial component 92 further comprises a stem94 with ribs 94′ configured to be anchored in a medullary channel of thetibia 99. The stem 94 is routed through the channel 11 of the tibialaugment 1.

On the top 12 the wall 17 meets a top cover 2 which covers the completetop. The top cover 2 and the wall 17 form a unitary piece. Thereby, thewall 17 in conjunction with the top cover 2 act as a bulkhead blockingany passage of cement from the channel 11 to an external side of thehollow sleeve 10. Optionally the wall 17 features a sandwich structurehaving a solid portion 18 and a porous portion 18′, wherein the porousportion 18′ forms an outer face 15 of the hollow sleeve 10. The porousportion 18′ is formed of porous material which is configured forpromoting ingrowth of bony material.

The porous portion 18′ is preferably made of a highly porous materialhaving a porosity of at least 60-90%. Preferably, its pores areinterconnected and elementary cells defining the pores are arranged in aregular order. The interconnected pores provide for a much improvedingrowth of bony material, and thereby ensure a good stabilization ofthe tibial augment 1 in the tibial bone 99.

For implantation cement may be applied for fixation of the stem 94. Thecement will be applied within the channel 11 around the stem 94. Inorder to preserve the positive bone ingrowth effect of the porousmaterial 17′, the cement shall not reach the outer face. For thispurpose the solid portion 18′ of the wall 17 is provided acting as abulkhead confining the cement to an inner portion, thereby keeping theouter face essentially cement-free. The top cover 2 ensures that nocement could spill over towards the top. A bottom cover is notnecessary. However, it may be provided at the section of the bottomoutward of and including the wall, thereby blocking any unwanted influxof cement into the porous material 18′ on the outer face.

For a tighter fit and in particular an improved removal in case of are-operation, the augment device 1 comprises bending joints 3, 3′ (notshown in FIG. 1). Two preferred variants of the augment device havingbending joints 3, 3′are shown in FIGS. 3 and 5. Both feature two sets ofbending joints 3, 3′ in different configurations. Generally speaking,the bending joints 3, 3′ allow a bending of the hollow sleeve 10 suchthat it will be compressed as a whole, thereby reducing the size of thechannel 11 and the outer dimension of the hollow sleeve 10. Each of thebending joints 3, 3′ is formed by a void 30 in the wall 17 combined witha metal strip 31 which spans the void 30. As best appreciated in FIG. 4,the metal strip 31 is of solid material and runs from the top 12 to thebottom 13 of the hollow sleeve 10. The metal strip 31 is configured suchas to provide the bending joint 3, 3′ with elasticity in respect to abending movement. By varying the dimensions of the metal strip 31 or bychoosing a different material the characteristics can be adjusted. Asshown in more detail in FIG. 4, the strip 31 is oriented oblique withrespect to the wall 17 such that a lower end 34 of the strip 31 ispositioned close toward the outer face 15 of the wall 17 and the upperend 32 of the strip 31 is placed close to the inner face of the wall 17.By virtue of this arrangement, the strip 31 is oriented essentiallyparallel to a center axis of the channel 11. Thickness of the strip 31at a lower portion 34 is reduced. To this end, the strip 31 isconfigured such as to have a tapering width towards its lower end 34. Byvirtue of this tapering, the most bending force will be created by theupper part of the strip 31, whereas the lower portion 34 will onlycontribute to the bending force to a much lesser degree.

The bending force and movement effected thereby is depicted in FIG. 3a .Two pairs of bending joint 3, 3′ are provided in a mirror symmetricconfiguration. A first set of bending joints 3 is placed at a rear wallof the hollow sleeve 10. By exerting a bending force, the bending joints3 allow for a movement in a rotational direction as indicated by thesingle arrow. Thereby an axis of bending defined by the bending joints 3provides for an elasticity in a medio/lateral (ML) direction.

A second set 3′ is provided which is arranged in a mirror symmetricconfiguration at the side portion of the hollow sleeve 10. The bendingjoints 3′ provide a range of motion as depicted by the double arrow.This provides for an axis of bending which gives anterior/posterior (AP)elasticity. As a result, by providing both pairs of bending joints 3, 3′elastic compressibility in two dimensions is achieved, namely one in MLdirection and another in AP direction. The center of rotation for thebending joints providing elastic compressibility in ML direction isshown with a symbol resembling a letter “X” whereas the elasticcompressibility in AP direction is shown by symbol resembling a cross ina circle, each showing the effective center of rotation.

In the variant as shown in FIG. 5 a, b the second set 3′ for providingelastic compressibility in AP direction (anterior/posterior) isidentical to that of the first variant depicted in FIG. 3 a, b. However,the first set of bending joints providing a range of motion inmedio-lateral (ML) direction is configured differently, namely as aconcentrated element in which the two bending joints 3 of FIG. 3a arecombined to one bending joint 3″ which has a wider dimension. Thefunctionality is essentially identical to FIG. 3 a, b, namely thebending joint 3″ provides elastic compressibility in ML direction.

By exerting bending force the width of the inner channel 11 will bereduced. Thereby, its circumference will be reduced. In order to enablethe hollow sleeve 10 for such a reduction, a compensator element 4 isprovided. In the depicted embodiments it is arranged at an opposite,front side of the hollow sleeve 10 to the bending joints 3. Thecompensator element is comprised of two tongues 41, 42 arranged at aleft and a right portion of the hollow sleeve 10. The tongues 41, 42 arearranged in an overlapping configuration, leaving just a tiny gap 43therebetween. The tongues 41, 42 slide along each other under the effectof a bending motion with the bending joints 3, 3′, thereby promotingcompressibility. The gap 43 is dimensioned such as to be small enough toblock leakage of cement.

As best shown in FIG. 6 a, b a set of receptacles 16 are provided in thevicinity of the top 12 of the wall 17. The receptacles 16, two of whichare placed on a front side of the augment device 1 at a left and rightportion and further two are placed on a back side of the augment device1 also at a left and a right portion. The front and the back side areshown in FIG. 6 a, b respectively. Receptacles 16 are configured asrecesses which are enabled to provide a form-fit with grippers of anextraction tool 5, as will be explained in detail further below.Further, alignment holes 21 are provided in the top cover 2 of theaugment device 1. The alignment holes 21 are configured as blind holeswhich are laterally open to the outer face 15. The alignment holes 21are configured for accepting alignment pins 81 of a jig 8. For refinedpositioning the alignment holes 21 are preferably slightly conical inshape, as it is shown in more detail in FIG. 7. Further, checking marks22 could optionally be provided at a top 12 of the augment device 1. Thechecking marks 22 are set in a fixed spatial relation to the alignmentholes 21. The checking marks 22 are configured such as to indicateproper positioning of the jig 8 in respect to the augment device 1. Thisact as a further means of checking whether the jig 8 is positionedcorrectly in respect to the augment device 1, thereby acting as averifying means in addition to the alignments holes 21.

The relation between the jig 8 and the augment device 1 in its implantedstate in a tibia 99 is shown in FIG. 8. The tibia 99 is shown withdashed lines. At its proximal end, the augments device 1 is positionedin a cavity. A top 12 of the augment device 1 is substantially flushwith the upper surface of the tibia 99. The jig 8 is provided with twoalignment pins 81 projecting downwards from a lower side 83, thealignment pins 81 being spaced such far apart as the spacing of the twoalignment holes 21 of the augment device 1 are spaced, and they areconfigured to being engaged in said alignment holes 21, therebyproviding a positive positioning of the jig 8 in respect to the augmentdevice 1. Proper positioning of the jig 8 in respect to the augmentdevice is important since the jig 8 is further provided with a pluralityof guiding holes 86 which are positioned at each corner of the jig 8.The guiding holes 86 indicate those positions, at which holes are to bebored in order to provide sufficient space for incursion of grippers 6of an extraction tool 5. The jig 8 is generally of a flat plate likestructure having a planar upper side 82 and a substantially planar lowerside 83. The four guiding holes 86 are arranged at the four corners. Inthe middle a large central opening 84 is provided in order to allow fullaccess to the inner channel 11 of the augment device 1. For manipulatingof the jig 8 a handle 80 is provided which is formed as a unitary pieceat a longer edge of the jig 8. On the opposite side the alignment pins81 are mounted such that they are projecting from the lower side 83 ofthe jig 8. Placing of the jig 8 onto the augment device 1 is illustratedby two arrows in FIG. 8, the arrows showing the alignment pins 81 andtheir trajectory into the alignment holes 21.

The extraction tool 5 for extracting the augment device 1 of the tibia99 is depicted in FIG. 9 a, b. It comprises a substantially flat frame50 having a center portion 52 and a periphery portion. The substantiallyflat frame 50 comprises a V-shaped stationary sub-frame 58 in the centerportion 52 and two movable outriggers 59 at a left and right peripheryportion. Each movable outriggers 59 is affixed by means of a swiveljoint to the respective outer end of the V-shaped stationary sub-frame58. The other ends of the outriggers 59 are connected with each other bya compression element 65. The compression element 65 is configured to becompressible upon actuation by an actuating tool (not shown); in thedepicted embodiment the compression element 65 is a double threaded nut66 riding along counter-threads of stubs 67 mounted at the free ends ofthe outriggers 59, thereby moving the two free ends of the outriggers 59toward each other in a planar fashion. At either end of both outriggers59 one gripper 6 is mounted, each gripper having teeth for engaging theaugment device 1. The grippers arranged in the stationary sub-frame 58are denominated by reference number 6, while those grippers arranged atthe movable elements, namely the outriggers 59 are denominated with areference number 6′. The grippers 6, 6′ are located at the four cornersof the substantial flat frame 50 and the movable grippers 6′ move in aplane defined by said frame 50.

It is important to note that the edges of the frame 50, including itsstationary sub-frame and the outriggers 59, are not coincident with animaginary envelope line 57 connecting the four corners 55; rather, theedges of the frame 50 with the sub-frame 58 and the outriggers 59 arebeing offset that, namely set-off towards the center portion 52. Byvirtue of this, access to the outer face 15 of the wall 17 of theaugment device 1 to which the extraction tool 5 is to be attached ismuch facilitated, since owing to the off-set configuration of its edgesthe frame 50 does not block access. This is depicted in FIG. 9a ,wherein the outline of the augment device 1 is shown by a dashed line.

The grippers 6, 6′ are provided with of engagement means for engagingthe augment device 1. One embodiment is to have teeth 62 at the lowerend of the gripper 6, 6′ which are configured for engaging into thereceptacles 16 of the augment device 1. In case no receptacles areprovided, then teeth 62 at the grippers 6, 6′ serve the purpose ofpiercing into the outer face 15 of the augment device, thereby engagingit and affixing the extraction tool 5 to the augment device 1. Analternative embodiment would be to have just projections withouttoothing, which would sufficient for engaging the receptable 16.Preferably, the grippers 6, 6′ are held at the corners 55 in such amanner that they are easily replaceable (s. FIG. 9b ).

In the stationary sub-frame 58 a central opening 58′ is provided whichis configured for being engaged by a holder 7. The holder 7 comprises ashaft 71 having a handle 70 at its rear end. At its front end the holder7 features a threaded tip 72 which can be brought into engagement with acomplementary thread at the center hole 58′. Optionally, a strikingweight 73 is slidably mounted at the shaft 71, for an amplified pull-outforce. The holder 7 is shown in FIG. 10 together with the jig 8, formingan instrument set in conjunction with the extraction tool 5 (FIG. 9 a,b).

The relation of the jig 8 to the extraction tool 5 and its holder 7 isshown in FIG. 11. The jig 8 is to be placed between the augment device 1on its top, and on the top of the jig 8 the extraction tool 5 is shown.

The method of operation for an inventive use of the instrument set andthe augment device accord to the present invention is shown stepwise inFIG. 12 a-h. In FIG. 12a a tibia 99 having an augment device 1 which isto replaced is shown. It is assumed that the augment device 1 isconnected quite strongly to the tibia 99, in particular by bony ingrowthinto a porous structure 18′ on the outer face 15 of the wall 17. Due tothat ingrowth removal of the augment device 1 is difficult. In a firststep shown in FIG. 12b , the jig 8 is to be brought into positionoverhead of the augment device 1. It is positioned such that itsalignment pins 81 on the lower surface of the jig 8 are in line with thealignment holes 21 of the augment device 1 (see dotted lines in FIG. 12b). FIG. 12c shows the jig 8 brought into position in an alignedrelationship, wherein the alignment pins 81 are centered in thealignment holes 21. The jig 8 is now sitting flat on the top of theaugment device 1. Its guiding holes 86 at its four corners define holesthat are to be drilled in order to make room for inserting the grippers6, 6′ at a later stage. Once these holes are drilled, the jig 8 may beremoved. The drilled holes after removal of the jig 8 are shown in FIG.12d . Then the extraction tool 5 is placed overhead of the augmentdevice 1 and positioned such that its grippers 6,6′ are aligned with thefour holes created by drilling through the guiding holes 86 (s. FIG. 12d). The extraction tool 5 can then be lowered into position on top of theaugment device 1, and the grippers 6, 6′ with their engagement means(teeth 62) will enter into the said drilled holes (s. FIG. 12e , pleasenote that FIG. 12 e-h depict a view from the opposite side). The teeth62 are now so far lowered as to be approximately at the height at whichthe receptacles 16 are placed at the augment device 1. In a next stepthe compression element 65 is actuated by a tool (not shown), and themovable grippers 6′ mounted on the outriggers 59 are brought into aninward position (s FIG. 12f ). As a result, the extraction tool 5 issecurely affixed to the augment device 1 by virtue of the engagementmeans (teeth 62) of the grippers 6, 6′ being engaged in the receptacles16. In principle the augment device 1 could now be removed by pulling onthe extraction tool 5. However, due to the bony ingrowth the augmentdevice 1 is likely to be held in position. In order to break the augmentdevice free, the compression element 65 is actuated further by the tool(not shown), namely so far that the bending joints 3 are moved and thewall 17 of the augment device 1 is compressed. Thereby the outercircumference of the wall 17 is decreased, producing a gap 97 betweenthe original cavity in which the augment device 1 was placed and theactual outer circumference of compressed augment device. Due to this gap97 any connection due to bony ingrowth between surrounding bony tissueand the porous outer face 15 of the augment device 1 will break away.Thereby the augment device 1 becomes free. Subsequently, it can bepulled out straight by the extraction tool 5, as shown in FIG. 12 h.

What is claimed:
 1. An augment device for a joint endoprosthesiscomprising: a hollow sleeve surrounding a channel extending through thehollow sleeve from a top to a bottom of the hollow sleeve, the hollowsleeve comprising a wall having an inner face, an outer face, and atleast one bending joint configured for compression of the channel,wherein the at least one bending joint is formed by an integral hingethat comprises an elongated void in the hollow sleeve and a strip ofsolid material spanning the void, wherein the strip is oriented suchthat a lower end of the strip is positioned closer to the outer facethan an upper end of the strip, and wherein the upper end of the stripis positioned closer toward the inner face than the lower end of thestrip.
 2. The augment device of claim 1, wherein the strip is orientedsuch as to be oblique with respect to the wall.
 3. The augment device ofclaim 1, wherein the strip comprises a tapering width towards the lowerend, in which the width at a lower portion of the strip is less than thewidth at an upper portion.
 4. The augment device of claim 3, wherein theat least one bending joint is configured to have a lower bendingstiffness in the lower portion as compared to the upper portion.
 5. Theaugment device of claim 1, wherein the at least one bending joint isarranged as to enable compression in a lateral-medial direction.
 6. Theaugment device of claim 1, wherein the at least one bending joint isarranged to enable compression in an anterior-posterior direction. 7.The augment device of claim 1, wherein the hollow sleeve comprises acompensator element configured for adjusting a circumference of thesleeve in a beaded state of the bending joint.
 8. The augment device ofclaim 1, wherein the hollow sleeve comprises receptacles for receiving ahandling tool.
 9. The augment device of claim 8, wherein the receptaclesare configured as recesses that may form-fit with the grippers.
 10. Theaugment device of claim 9, wherein the receptacles include an under-cut.11. The augment device of claim 1, wherein the top of the hollow sleeveincludes alignment holes that are configured for positioning a jig. 12.The augment device of claim 11, further comprising checking markslocated in a fixed spatial relation to the alignment holes, the checkingmarks being configured to indicate proper positioning of the jig. 13.The augment device of claim 1, wherein the wall is a sandwich structurehaving a solid portion and a porous portion, the porous portion formingthe outer face and being formed of porous material which is configuredfor ingrowth of bony material.
 14. The augment device of claim 1,further comprising a top cover made of solid material and configured tocover the top of the hollow sleeve.
 15. The augment device of claim 14,wherein the top cover and the wall form a unitary element.
 16. Theaugment device of claim 1, wherein the wall is at least partiallycomprised of porous material configured for promoting bone ingrowth. 17.The augment device of claim 1, wherein the augment device is a tibialaugment for a knee joint endoprosthesis.
 18. The augment device of claim1, wherein the one or more bending joints are arranged in mirrorsymmetry.
 19. The augment device of claim 7, wherein the compensatorelement is configured as two overlapping tongues arranged in a slidingrelationship.